This invention relates generally to dissolved air flotation (DAF) water clarifying systems and, more particularly to a liquid inlet structure for intimately mixing the recycle, or secondary, flow with the primary, or raw, flow at the start of the treatment process.
In wastewater treatment by dissolved air flotation, suspended solids particles adhere to or are entrapped by gas bubbles. Raw wastewater is fed into the flotation device and must be mixed with a recycle flow which is saturated with air and contains air bubbles. The efficiency of the system is directly dependent on the thoroughness of the mixing of the raw and secondary flows taking place at the start of the flotation process.
Prior flotation devices of the type described employed common "Y" or "T" fittings for the introduction and mixing of the two liquid streams. Typically, the raw wastewater was directed through a main pipe having a secondary inlet pipe attached directly thereto in the form of a "Y" or "T", and the recycle flow was introduced through the converging/secondary inlet pipe. It has been found that acceptably efficient mixing of the two liquid streams may not be achieved under normal low pressure operating conditions. While high liquid entry velocities tended to improve mixing, those conditions may result in undesirable liquid shear affecting flocculated solids commonly present in the raw waste stream.
There thus exists a need for a more efficient means of mixing the primary wastewater and secondary recycle flows of DAF treatment systems.